418 DR S. F. HARMER AND DR. W. G. RIDEWOOD ON THE 



from the soft general material of the crencecium. This is in conformity with what 

 one sees at the apex of a branch, where the very young tubes have no spines (text- 

 fig. 2, A). 



The part drawn in text-fig. 2, B, shows four spines which have no ostia alongside 

 (e.g. s). Three of these spines did not reach the surface, but had been buried over 

 during the increase in the thickness of the branch. Occasionally, but rarely, a buried 

 spine is found to have a closed-up tube by its side. Such an occluded tube is closed 

 by a thin, curved partition, such as is seen in some of the inner tubes (as at 5 and s' in 

 text-fig. 2, A), the convexity in the present case being towards the outer surface ; and 

 over this and also over the spine the soft material of the coenoecium is deposited 

 uniformly. One must suppose that in this case the tube was not occupied at the time 

 that the zooids in the immediate vicinity were lengthening their tubes and filling in 

 the intervals between them, and that the septum was formed subsequently from 

 within. The relations of the spine alongside the occluded tube, and the succession of 

 caps composing the spine, prove that the blind end of the tube is a closed-up ostium, 

 and is not the initial end of a tube, blind from the commencement, such as one sees in 

 the middle part of a branch of C. nigrescens (07 1 , pi. iv. fig. 10). 



Although the present species is denominated O. ayglutinans, from the manner in 

 which the zooids have embedded great quantities of shelly fragments in the material of 

 the coenoecium, the habit is not peculiar to this species, for HARMER has stated in his 

 account of the new species which were obtained on the Siboga Expedition (05, p. 8), 

 that the cosnoacium includes foreign particles as a rule, and that they are specially 

 obvious in C. sibogse (05, pi. ii. fig. 17, 18). ANDERSSON quotes as one of the characters 

 by which C. solidus is distinguishable from C. rarus, that the tubes are encrusted with 

 sand, diatoms, etc. (07, pp. 11, 12) ; and he further states that the tubes of C. densus 

 are covered with sand-grains. GRAVIER, again (12, p. 2), says that in C. anderssoni 

 (which, if not synonymous with C. densus, is very closely allied to it) sand-grains and 

 shells of Foraminifera resembling Polystotnella adhere to the outer face of the tubes, 

 and are even incorporated in the substance of the wall. The basal parts of the pieces 

 of colony of C. nigrescens are also known to contain fragments of shells (RIDEWOOD, 

 12, p. 551, Specimen C). 



The inclusions in the coenoecium of C. agglutinans are present in such quantity as to 

 make the branches of the colony much more readily crumbled and broken than are those 

 of C. nigrescens, which in general massiveness bear some resemblance to the branches 

 of the present species. The particles included are mostly calcareous, and disappear 

 when a branch is soaked in a 1 per cent, solution of nitric acid for ten days or a 

 fortnight. The only foreign particles remaining after this treatment are some rounded, 

 dark grey, or blackish grains, which Dr J. W. EVANS, Mineralogist of the Imperial 

 Institute, has been good enough to examine for us. He reports that they are water- 

 worn grains of slate. They mostly vary in size from '3 to 1 mm. in diameter, but one 

 was found as large as 6 mm. across. A few of them are paler in colour, and softer, 



(HOY. soc. EDIN. TRANS., VOL. XLIX., 542.) 



